Polycarbonates have been known for a number of years. U.S. Pat. No. 3,301,824 (1967) describes the preparation of carbonate homopolymers and random copolymers with cyclic lactones. While the patent generally discloses the polymers as having utility as moldings, coatings, fibers and plasticizers, there is no appreciation whatsoever of biodegradable fibers composed in whole or in part of such polycarbonates.
In addition, there is no appreciation for the usefulness and importance of substituted polyaliphatic carbonates as fiber forming polymeric compositions since in the above patent, it is caprolactone, the dominant co-monomer, which offers the necessary crystalline character needed for fiber formation.
U.S. Pat. Nos. 4,243,775 (1981) and 4,429,080 (1984) disclose the use of aliphatic carbonate-containing polymers in certain medical applications as sutures and medical fasteners. However, this disclosure is clearly limited only to "ABA" and "AB" type block copolymers where only the "B" block contains poly (trimethylene carbonate) or a random copolymer of glycolide with trimethylene carbonate. The A block is necessarily limited to polyglycolide, which is the only component to confer the crystalline character in the polymer (necessary for fiber formation); and the major portion of the polymers is the glycolide.
Accordingly, the art has failed to fully appreciate the potential biological or medical uses of biopolymers based on aliphatic carbonates, especially with respect to their biodegradable or bioresorbable properties, as well as the range of mechanical properties achievable with these materials.
Bioresorbable polymers have been used in the fabrication of devices for implantation in living tissue for several decades. Medical application of such polymers include absorbable sutures, haemostatic aids and, recently, intraosseous implants and slow-released drug delivery systems, to name but a few.
Use of such polymers has been extended to tissue regeneration devices such as nerve channels, vascular grafts, sperm duct channels, fallopian tube ducts or channels and the like. To be effective, these devices must be made from materials that meet a wide range of biological, physical, and chemical prerequisites. The material must be bioresorbable at least in part, nontoxic, noncarcinogenic, nonantigenic, and must demonstrate favorable mechanical properties such as flexibility, suturability in some cases, and amenability to custom fabrication. The biopolymers of the present invention have all of these attributes.